Anti-biofouling seismic streamer casing and method of manufacture

ABSTRACT

An anti-biofouling seismic streamer casing ( 100,100′ ) is provided that is formed by a flexible tubing ( 110 ) coated with a layer of a two-part heat cured silicone elastomer ( 120 ). The seismic streamer casing ( 100, 100′ ) is formed by a method that includes steps of providing a flexible tubing ( 200 ) and pre-treating the outer surface of the tubing ( 210 ). Two parts of a two-part silicone elastomer are then mixed together ( 220 ). The method also includes coating the mixed two-part silicone elastomer on the flexible tubing ( 230 ), and heating the flexible tubing to cure the coating ( 240 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention directs itself to anti-biofouling coatings. In particular, this invention is directed to an anti-biofouling coating for a flexible tubing material to produce seismic streamer casings. Further, this invention is directed to a method forming a seismic streamer casing wherein a two-part, heat cured, silicone elastomer is applied to a flexible tubing that has been pretreated to increase the adhesion of the coating to the flexible tubing.

2. Prior Art

Marine biofouling on the hulls of ships has been a problem for centuries. More recently, as more undersea sensors and robotic systems have been utilized for extended periods of time, the control of biofouling has become more critical. Historically, anti-biofouling coatings utilized biocides that leach out from the coating over time to thereby prevent biofouling settlement by virtue of the biocides toxicity to marine organisms. This method of control has had a number of problems associated therewith. First, the biofouling resistance of the coating decreases with time as the biocides are depleted by their leaching out. Furthermore, the toxic coatings increase the danger of toxic exposure to shipyard workers, create a hazardous waste disposal problem, and have a detrimental environmental impact on marine wildlife.

The use of some elastomer based coatings resist fouling by presenting a surface that is unsuitable for strong adhesion of the fouling organisms. While silicone coatings have an inherent non-stick nature, it has been possible to provide satisfactory adhesion between silicone coatings and relatively rigid substrates by the use of one or more intermediate primer layers to provide a bond between the substrate, such as a boat hull, and the silicone outer layer. The silicone elastomer that has traditionally been utilized in these systems is of the room temperature vulcanizing type, also known as condensation cured silicone elastomers.

The best prior art known to the Applicants include U.S. Pat. Nos. 2,986,474; 3,973,510; 3,987,537; 4,025,693; 4,072,769; 4,312,693; 4,844,986; 4,894,254; 5,449,553; 5,691,019; 6,101,973; 6,221,498; 6,348,237; 6,403,105; and, 6,570,821, and published U.S. Patent Applications 2001/0032568 and 2004/0017731. None of the prior art systems disclose a two-part, heat cured silicone elastomer that is applied to a flexible tubing material for providing anti-biofouling. Additionally, the known prior art does not disclose a method for applying a silicone elastomer anti-biofouling coating in a continuous automated process.

SUMMARY OF THE INVENTION

A seismic streamer casing is provided that includes a flexible tubing coated with a layer of a two-part heat cured silicone elastomer to provide anti-biofouling therefore. The seismic streamer casing is formed by a method that includes steps of providing a flexible tubing and mixing together two parts of a two-part silicone elastomer. The method also includes coating the mixed two-part silicone elastomer on the flexible tubing, and heating the cured flexible tubing to cure the coating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a marine seismic exploration system in which the invention of the subject Patent Application may be utilized;

FIG. 2 is a cross sectional view of the seismic streamer casing of the present invention;

FIG. 3 is a cross sectional view of another configuration of the seismic streamer casing of the present invention;

FIG. 4 is a block diagram of the method of the present invention;

FIG. 5 is a block diagram illustrating the manufacturing processes for manufacturing the present invention;

FIG. 6 is a block diagram illustrating the variation of the manufacturing processes for the present invention; and

FIG. 7 is a schematic diagram illustrating the method for manufacturing the seismic streamer casing of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown an exploration ship 10 towing a seismic streamer 20. Subsea geologic research and oil exploration is carried out through the use of vessels like the ship 10 which use acoustic pulses that are transmitted from the ship and through the water to penetrate the sea floor. The acoustic reflected return signals are received by the one or more seismic streamers 20 that are towed behind ship 10. Typically, a ship would tow an array of seismic streamers consisting of five to eight flexible tubular structures that are filled with an oil or a buoyant solid material and a plurality of sensors for receiving the acoustic return signals. The oil adds buoyancy to the seismic streamer and may also function as a dielectric.

Seismic streamers have a casing that may be formed of one or more layers. An outermost layer of a multilayer construction may be a sheath that is sleeved over an underlying tubular structure during assembly of the streamer. The underlying tubular structure may be an oil filled tube or a solid core with the internal electronic assemblies are molded in the solid core. As used herein, it is to be understood that the seismic streamer casing is the outermost tubular structure of a seismic streamer assembly, whether it is a sheath that is sleeved over another tube or solid core, or a single or multilayer tube that is itself filled by sensors and buoyant material.

The casing of the seismic streamers is formed of a flexible plastic material, such as polyurethane, and typically has a diameter of within the approximating range of 2 to 2.5 inches. The length of a seismic streamer may be as little as 100 feet, however, seismic streamers that are typically used for oil exploration have a length approximating 10 to 15 kilometers. The streamers are towed through the water at a depth that ranges from 5 to 15 feet, and they remain in the water for periods as long as 8 months.

Although materials such as polyurethane have an outer surface that is not easily adhered to, they are subject to biofouling. The adherence of barnacles to the seismic streamer causes unacceptable levels of hydrodynamic drag and also disrupts the positioning of the streamers in tow such that reception of the acoustic signals is compromised. In order to overcome this problem, the invention of the subject patent application provides a seismic streamer casing 100, as shown in FIG. 2. Seismic streamer casing 100 includes a flexible tubing 110 having an outer layer 120 formed by a two-part heat cured silicone elastomer. The silicone elastomer layer 120 has a thickness within the approximating range of 0.0001 to 0.20 inches. The flexible wall of the tubing 110 surrounds a through-bore 105 into which the oil and instrumentation of the seismic streamer is received and has a thickness within the approximating range of 1/32 to ¼ of an inch. The elastic material which forms the tubing 110, in addition to being flexible, must be hydrocarbon resistant to avoid degradation from contact with the oil which is contained within the seismic streamer. Tubing 110 may be formed of materials such as urethane, polyurethane and polyvinylchloride, with polyurethane being the most widely used material for seismic streamers used for oil exploration.

As previously noted, the surface of the tubing 110 is not very conducive to providing adhesion with other materials. Likewise, silicone elastomers generally do not exhibit strong adhesive qualities. To overcome these short comings, some form of pretreatment may be utilized to provide strong bonding of the silicone elastomer to the tubing 110. In the embodiment of FIG. 2, any pretreatment is in the form of a physical modification to the surface contours of the tubing 110. The types of pretreatment suitable for application to tubing 110 will be described in following paragraphs.

In the configuration shown in FIG. 3, the seismic streamer casing 100′ is formed with the same tubing 110 having a through-bore 105 and a two-part heat cured silicone elastomer 120. Additionally, seismic streamer casing 100′ includes a intermediate layer 115, defining a tiecoat that is utilized to enhance the bonding between the silicone elastomer and the outer surface of the flexible material composition which forms tubing 110. This tiecoat 115 is a commercially available product which increases the bonding strength and toughness of the silicone elastomer. The use of one or more tiecoating layers may be combined with physical surface modification to further enhance adhesion between the layers. However, the flexibility of the material of tubing 110, as compared to the rigid substrates to which silicone elastomers have conventionally been applied as anti-biofouling coatings, requires the tiecoat composition to be equally flexible. Thus, the tiecoat compositions conventionally used in marine applications have not been found to be suitable for use in preparing seismic streamer casings, as they to not have the necessary flexibility. Tiecoat compositions formed by urethane or polyurethane based adhesive compositions may be used as tiecoat 115.

Turning now to FIG. 4, there is shown a block diagram of the method of manufacturing the seismic streamer casing of the instant invention. In step 200, the flexible tubing is provided. As previously discussed, the polyurethane tubing is currently the commonly used material for seismic streamers. The tubing may be provided in predetermined lengths, i.e. 40 to 15,000 meters, for direct use by an end user. Alternately, the tubing may be provided in greater lengths and subsequently cut to the desired length subsequent to the curing process. If the flexible tubing is to be pretreated, which improves the bonding strength between the flexible tubing and the elastomer, the next step is 210, otherwise the process jumps to step 220.

In step 210 the flexible tubing is pretreated in order to improve the bonding between the flexible tubing and the silicone elastomer coating. The pretreatment consists of the use of mechanical or chemical means to modify the physical surface characteristics of the flexible tubing. Mechanical surface preparation may include etching of the surface by abrasion, laser ablation, particulate or fluid blasting, or plasma treatment. Chemical etchents, applied by a number of well known techniques, may also be utilized to physically alter the surface characteristics of the flexible tubing. The pretreatment process of step 210 may additionally or alternately include the application of tiecoat layer as a primer.

In step 220, the two parts A and B of the silicone elastomer are mixed. The parts A and B of the elastomer represent a polysiloxane polymer and a platinum catalyst. Suitable silicone elastomers for the practice of the instant invention are available from Dow Corning Corporation having the designation Silastic 590, 591, 592, 593, 594 and 595 and the General Electric Company having the designations SLE 5100, SLE 5300, SLE 5400, SLE 5500, and SLE 5600.

In step 230, the mixed silicone elastomer is coated on the flexible tubing. The methods for coating the tubing with the mixed silicone elastomer, to be discussed in following paragraphs, include spraying, brushing, dip coating, extrusion and flow coating. The coating process is enhanced by the pressurization of the tubing so that the flexible tubing maintains a constant and uniform contour throughout its length as it undergoes the coating process. Subsequent to coating, the coated tubing, in step 240, is exposed to heat for a predetermined time period, within the range of 1 to 30 minutes at a temperature in the range of 200 to 500 degrees Fahrenheit, to promote and/or accelerate the curing of the silicone elastomer coating.

Referring now to FIG. 5, there is shown a block diagram of a manufacturing process for producing the seismic streamer casing of the present invention. The process begins with the supply of flexible tubing 300 which, owing to the long lengths of the tubing required, is provided wound about a spool. The tubing is unwound from the spool and may be pretreated in order to increase the adhesion between the surface of the tubing and the silicone elastomer that will be subsequently applied. Pretreatment 310 can take a number of forms, as previously discussed. In one working embodiment of the method of the present invention, a plasma treatment was utilized to prepare the surface of a polyurethane tubing substrate. The outer surface of the tubing is passed in proximity to a plurality of symmetrically disposed electrodes wherein it is exposed to a high voltage corona discharge.

Subsequent to the pretreatment step, the ends of the tubing are sealed in step 320 and the tubing pressurized so that it maintains a uniform cylindrical contour as it is being processed to apply the elastomer coating thereto. The pressurization of the flexible tubing aids in maintaining a circular cross sectional contour of the tubing as it is coated, thereby providing uniformity of that processing by virtue of the geometry of the tubing. The silicone elastomer is applied in step 330. While any of the aforesaid methods of silicone elastomer coating application may be utilized, a variation of a dip coating process has been successfully used to coat the pretreated polyurethane tubing substrate, and will be discussed with respect to the process illustrated in FIG. 7 in following paragraphs.

Subsequent to the application of the silicone elastomer in the step 330, the coated tubing is then moved through a curing oven, in step 340, to heat the silicone elastomer to promote and/or accelerate the curing thereof. The curing oven heats the silicone elastomer to a temperature within the range of 200 to 500 degrees Fahrenheit and for a time period within the range of 1 to 30 minutes.

An alternate arrangement of the manufacturing process is shown in FIG. 6. In FIG. 6, the tubing sealing and pressurization step 320 is carried out while the flexible tubing is still substantially wound on the reel. By this manufacturing method, the pressurization of the flexible tubing occurs prior to the pretreatment step 310. The pressurization of the flexible tubing acts to ensure that the surface treatment occurs uniformly about the surface of the tubing by maintaining the cross sectional contour of the tubing substantially constant, as it does during the coating process. The uniformity of the physical surface treatment contributes to the improved adhesion between the flexible tubing and the silicone elastomer. Therefore, it can be seen that the pressurization of the tubing substrate is important to the processing of the flexible tubing to produce an anti-biofouling seismic streamer casing. The subsequent pretreatment 310, silicone elastomer application 330 and heat curing processes 340 are identical to those previously described.

In FIG. 7, an exemplary manufacturing process for seismic streamer casings is shown schematically. The process for providing the seismic streamers of the instant invention is a continuous process for sequentially carrying out the steps of the inventive method described herein. In the particular manufacturing process implemented in FIG. 7, the flexible tubing 412 being processed is wound on a supply spool 410. Prior to initiating the process, the opposing ends of the tubing, while on the spool, are sealed and tubing pressurized from a pressurized fluid source 400. Pressurized fluid source may be a air compressor or bottled source of compressed gas, such as nitrogen, or air. The pressurized fluid may be a liquid as well. The use of a liquid to pressurize the tubing may add additional steps of draining the fluid and drying the interior of the tubing, unless the liquid is the seismic streamer oil or a compatible liquid.

The pressurized flexible tubing 412 is first passed through a pretreatment chamber 420. As discussed earlier, one method of pretreatment that has been successfully utilized is a plasma treatment, however, other methods of physically altering the surface such as abrasion, laser abolition, and chemical etching may also be utilized. The treated tubing 422 moves from the pretreatment chamber 420 to a coating tank 430. The treated tubing 422 moves vertically through the coating tank 430, passing through a seal located at the bottom end of the tank. Coating tank 430 is supplied from an elastomer supply 440 wherein the parts A and B are mixed prior to their passage to the coating tank 430.

The coated tubing 432 continues vertically to a curing oven 450, wherein the tubing is maintained at the proper curing temperature, within the range of 200 to 500 degrees Fahrenheit, for the time period necessary to cure the silicone elastomer. Thus, if the required curing time is 20 minutes and the tubing is displaced at the rate of 1 foot per minute, the curing oven will have an overall height of approximately 20 feet to allow the tubing to have an adequate exposure to the curing temperatures. From curing oven 450, the seismic streamer casing 452 is provided to a winding spool 460 for subsequent transport to an end user. The supply spool 410 may carry an overall length of tubing for a single streamer, or a sufficient quantity for multiple streamers. Where the supply spool carries material for multiple streamers, a cutting operation may be interposed between the curing oven 450 and winding spool 460, such that each of a plurality of winding spools 460 are provided with a single seismic streamer casing wound thereon.

Although this invention has been described in connection with specific forms and embodiments thereof, it will be appreciated that various modifications other than those discussed above may be resorted to without departing from the spirit or scope of the invention. Equivalent elements or process steps may be substituted for those specifically shown and described, certain features may be used independently of other features, and in certain cases, particular locations of elements or sequence of process steps may be reversed or interposed, all without departing from the spirit or scope of the invention as defined in the appended claims. 

1. A seismic streamer casing comprising a flexible tubing coated with a layer of a two part heat cured silicone elastomer to provide anti-biofouling therefore.
 2. The streamer casing as recited in claim 1 wherein said flexible tubing is formed of polyurethane.
 3. A method of forming a seismic streamer casing comprising the steps of: a. providing a flexible tubing; b. mixing together two parts of a two part silicone elastomer; c. coating said mixed two part silicone elastomer on said flexible tubing; and, d. heating said coated flexible tubing.
 4. The method as recited in claim 3, wherein the step of providing flexible tubing includes the step of pre-treating a surface of said flexible tubing.
 5. The method as recited in claim 4, wherein the step of pre-treating is preceded by the step of pressurizing said flexible tubing.
 6. The method as recited in claim 4, wherein the step of pre-treating includes the step of forming a roughened surface on said flexible tubing.
 7. The method as recited in claim 3, wherein the step of coating is preceded by the step of pressurizing said flexible tubing.
 8. The method as recited in claim 3, wherein the step of coating includes the step of spraying said mixed two part silicone elastomer on said flexible tubing.
 9. The method as recited in claim 3, wherein the step of coating includes the step of brushing said mixed two part silicone elastomer on said flexible tubing.
 10. The method as recited in claim 3, wherein the step of coating includes the step of dip coating said mixed two part silicone elastomer on said flexible tubing.
 11. The method as recited in claim 10, wherein the step of dip coating includes the step of passing said flexible tubing substantially vertically through a reservoir of said mixed two part silicone elastomer.
 12. The method as recited in claim 3, wherein the step of coating includes the step of flow coating said mixed two part silicone elastomer on said flexible tubing.
 13. The method as recited in claim 7, wherein the step of coating includes the step of spraying said mixed two part silicone elastomer on said flexible tubing.
 14. The method as recited in claim 7, wherein the step of coating includes the step of brushing said mixed two part silicone elastomer on said flexible tubing.
 15. The method as recited in claim 7, wherein the step of coating includes the step of dip coating said mixed two part silicone elastomer on said flexible tubing.
 16. The method as recited in claim 7, wherein the step of coating includes the step of flow coating said mixed two part silicone elastomer on said flexible tubing.
 17. The method as recited in claim 14, wherein the step of dip coating includes the step of passing said flexible tubing substantially vertically through a reservoir of said mixed two part silicone elastomer. 